Revision summary
Glaciers erode by plucking and abrasion, turning V-valleys into U-troughs. Cirques, horns, arêtes, hanging valleys, and roches moutonnées are erosional forms. Till and moraines (terminal, lateral, medial, ground) are dumped at and under the ice. Meltwater builds outwash, kames, and kettles; erratics travel far. Himalayan glaciers show the same suite, with moraine lakes as a hazard.
Model answer
Introduction
Glaciers are slow rivers of ice. In high mountains they grind the rock they rest on and dump the debris they carry, so they both sculpture and build landforms above the snowline and in the valleys below.
Body
Erosional work
- Ice plucks jointed rock and abrades the bed with embedded debris, producing striations, polished pavements, and a U-shaped trough in place of a pre-glacial V-shaped river valley.
- Cirques (cwms) are armchair hollows at the head of the ice; when three cirques cut back they leave a pyramidal horn, and a knife ridge or arête between two cirques.
- Hanging valleys of tributary ice stand above the main trough and later become waterfall sites; truncated spurs replace interlocking river spurs.
- Roches moutonnées, glacial stairways, and over-deepened rock basins (later lakes) mark the bed; fjord-like drowned troughs appear where a glaciated valley meets the sea, though the Himalaya is more a land-ice theatre.
- In the Himalaya, the Gangotri, Siachen, and other valley glaciers keep these forms at high altitude; freeze–thaw on nunataks adds shattered debris to the ice.
Depositional work
- Till is unsorted debris dropped by melting ice; a terminal moraine ridges the farthest snout, laterals line the valley walls, and a recessional train marks still-stands of retreat.
- Medial moraines form where laterals join below a confluence; ground moraine carpets the floor as boulder clay.
- Outwash plains and valley trains of stratified sand and gravel are built by meltwater beyond the ice; kettle holes and kame terraces belong to this fluvioglacial suite.
- Erratics—far-travelled blocks—sit on unlike bedrock; drumlins and eskers are rarer in steep Himalayan valleys than on continental shields, but moraines and outwash are common in Kashmir, Garhwal, and Nepal valleys.
- Glacial lakes dammed by moraines (a risk in the Himalaya as GLOFs) are landforms of ice deposition as much as of water.
Role in one line of process
- High-mountain relief is therefore a partnership: ice steepens heads and walls, meltwater sorts the dump, and later rivers inherit the trough.
Flow diagram
flowchart TD I[Valley glacier] --> E[Cirque horn U trough] I --> D[Moraine till outwash] E --> R[High mountain relief] D --> R
Conclusion
Glaciers shape high mountains by plucking and abrasion into cirques, horns, arêtes, and U-troughs, and by dumping moraines, till, and outwash below the snout. Himalayan valleys display that erosional–depositional pair, including moraine-dammed lakes.
Quick related
Students also ask
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Do glaciers only erode?
No. They erode at the head and bed and deposit till and outwash at the snout and sides. Both make landforms.
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Is a Himalayan river gorge a glacial form?
Many deep Himalayan gorges are fluvial, cut after ice retreat. True glacial signatures are U-troughs, cirques, and moraines at higher reaches.
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